The present invention relates to a method and apparatus for reducing NO.sub.x in exhaust gases from an exhaust-gas-recirculation type fluidized-bed boiler.
FIG. 1 shows a conventional fluidized-bed boiler and a designates a boiler main body. Combustion air c from a forced draft fan b, which inhales the atmospheric air, is charged into a lower air chamber d and rises through an air distributor e (air injection nozzles) with small holes to fluidize granular particles, thereby forming a fluidized bed f over the distributor e for combustion of coal or the like. Exhaust gases g are discharged through an induced draft fan h.
In the fluidized-bed boiler of the type described, it has been proposed to provide an exhaust-gas mixing pipe k so that part of the exhaust gases g are mixed with the combustion air c through a dust collector i and an exhaust-gas mixing fan j, thereby reducing the amount of NO.sub.x in the exhaust gases g.
However, in such conventional system, there arises a problem that the dust collector i, which is provided to prevent wear of the air distributor e due to dust, to prevent the clogging thereof with dust and to protect the fan j, becomes very large in size because only a mechanical dust collecting system can be employed due to high temperature of the exhaust gases g. Furthermore there is a problem that the dust collection efficiency is low. In addition, because of part of high-temperature exhaust gases g being mixed with the combustion air c almost at room temperature, the temperature of the gases g drops to a cold corrosion temperature range so that cold corrosion of the combustion air supply system results.
The present invention was made to overcome the above and other problems encountered in the conventional fluidized-bed boilers and has for its object to prevent wear by dust of pipe lines and equipment used to recirculate and mix the exhaust gases with the combustion air and to prevent cold corrosion, thereby reducing NO.sub.x in the exhaust gases from the fluidized-bed boiler.
The effects, features and advantages of the present invention will become more apparent from the following description of a preferred embodiment thereof taken in conjunction with the accompanying drawings.